As a two-dimensional array X-ray detector that is used for an X-ray imaging apparatus, for example, a flat panel detector (FPD) is known. The flat panel detector has a configuration in which, on a substrate on which switching elements such as TFTs are arranged in a two-dimensional array (matrix), a converting film made of a-Se (amorphous selenium) or the like is evaporated. In the flat panel detector, when an image of X-rays passing through a test object is projected onto the converting film, charge signals proportional to shading of the image are generated in the converting film. The charge signals are collected by pixel electrodes that are arranged in a two-dimensional array and accumulated in electrostatic capacitors (capacitors). Charges accumulated in the electrostatic capacitors are read as the switching elements are operated, and transmitted to an image processing part as electrical signals, where image processing is performed (see Patent literature 1).